Medium [CVE-2025-4877] Libssh: write beyond bounds in binary to base64 conversion functions
This medium-severity Red Hat Linux advisory covers CVE-2025-4877 affecting Red Hat Enterprise Linux 9, Red Hat package: libssh.
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Summary
There's a vulnerability in the libssh package where when a libssh consumer passes in an unexpectedly large input buffer to ssh_get_fingerprint_hash() function.
In such cases the bin_to_base64() function can experience an integer overflow leading to a memory under allocation, when that happens it's possible that the program perform out of bounds write leading to a heap corruption. This issue affects only 32-bits builds of libssh.
Red Hat Product Security classified this vulnerability as having a Moderate severity. This happens because of the complexity of the attack, the possible misusage of the libssh API and the fact the attacker may not have full control over the positions and contents written into the heap.
No supported Red Hat products are affected by this issue since only 32-bit builds are vulnerable. Weakness: CWE-787.
Affected Red Hat products: Red Hat Enterprise Linux 9. Red Hat fixing advisory: RHSA-2026:18683.
Affected products named by the advisory: Red Hat package: libssh.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
- libssh-0:0.10.4-18.el9
- RHSA-2026:18683
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation
Upgrade to a fixed release: libssh-0:0.10.4-18.el9, RHSA-2026:18683. That is the remediation for this advisory.
The vendor advisory may list additional interim mitigations or workarounds not captured here — review it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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